The present invention relates to a nitride semiconductor growth method, a nitride semiconductor substrate, and a nitride semiconductor device and, more particularly, to a method of growing a nitride semiconductor having good crystal quality by using a substrate made of a material different from a nitride semiconductor, a nitride semiconductor substrate, and a nitride semiconductor device.
It is generally known that a semiconductor having few crystal defects and good crystallinity is grown on a substrate by using a substrate lattice-matched with the semiconductor to be grown. There is, however, no substrate that is lattice-matched with a nitride semiconductor, has excellent crystallinity, and allows a nitride semiconductor crystal to be stably grown. For this reason, there is no choice but to grow a nitride semiconductor on a substrate, e.g., a sapphire, spinnel, or silicon carbide substrate, that is not lattice-matched with nitride semiconductors.
Various research institutes have made attempts to manufacture GaN bulk crystals that are lattice-matched with nitride semiconductors. However, it has only been reported that GaN bulk crystals having sizes of several millimeters are obtained. That is, any practical GaN bulk crystal like the one from which many wafers are cut to be actually used as substrates for the growth of nitride semiconductor layers has not been obtained.
As a technique of manufacturing GaN substrates, for example, Jpn. Pat. Appln. KOKAI Publication Nos. 7-202265 and 7-165498 disclose a technique of forming a ZnO buffer layer on a sapphire substrate, growing a nitride semiconductor on the ZnO buffer layer, and dissolving and removing the ZnO buffer layer. However, since the ZnO buffer layer grown on the sapphire substrate has poor crystallinity, it is difficult to obtain a nitride semiconductor crystal having good quality by growing a nitride semiconductor on the buffer layer. In addition, it is difficult to continuously grow a nitride semiconductor thick enough to be used as a substrate on the thin ZnO buffer layer.
When a nitride semiconductor electronic element used for various electronic devices such as a light-emitting diode (LED) device, a laser diode (LD) device, and a light-receiving device is to be manufactured, if a substrate made of a nitride semiconductor having few crystal defects can be manufactured, a new nitride semiconductor having few lattice defects and forming a device structure can be grown on the substrate. Therefore, the obtained device acquires greatly improved performance. That is, a high-performance device that has not been realized in the past can be realized.
It is, therefore, an object of the present invention to provide a method of growing a nitride semiconductor crystal having excellent crystallinity.
More specifically, it is an object of the present invention to provide a method of growing a nitride semiconductor crystal that can provide a nitride semiconductor substrate, a nitride semiconductor substrate, and a nitride semiconductor device formed on the nitride semiconductor substrate.
According to a first aspect of the present invention, there is provided a nitride semiconductor growth method comprising the steps of (a) forming a first selective growth mask on a support member made up of a dissimilar substrate made of a material different from a nitride semiconductor and having a major surface, and an underlayer made of a nitride semiconductor formed on the major surface of the dissimilar substrate, the first selective growth mask having a plurality of first windows selectively exposing an upper surface of the underlayer of the support member, and (b) growing nitride semiconductor portions from the upper surface portions, of the underlayer, which are exposed from the windows, by using a gaseous Group 3 element source and a gaseous nitrogen source, until the nitride semiconductor portions grown in the adjacent windows combine or unite with each other on an upper surface of the selective growth mask. In this case, the total area of upper surfaces of portions, of the underlayer, which are covered with the first selective growth mask is preferably larger than that of portions, of the underlayer, which are exposed from the first windows.
According to a second aspect of the present invention, there is provided a nitride semiconductor growth method comprising the steps of (a) forming a first selective growth mask on a support member comprising a dissimilar substrate made of a material different from a nitride semiconductor and having a major surface, the first selective growth mask having a plurality of first windows for partly exposing an upper surface of the support member, such that a total area of upper surfaces of portions, of the support member, which are covered with the first selective growth mask is larger than that of portions, of the support member, which are exposed from the first windows, and (b) growing first nitride semiconductor portions from the upper surface portions, of the support member, which are exposed from the windows, by using a gaseous Group 3 element source and a gaseous nitrogen source, until the nitride semiconductor portions grown in the adjacent windows combine or unite with each other on an upper surface of the selective growth mask.
In the first and second aspects of the present invention, the first selective growth mask is preferably made up of a plurality of individual or discrete stripes spaced apart from each other, defining the first windows therebetween, and extending parallel to each other. In addition, in the first and second aspects, the ratio of a width of each of the stripes to a width of each of the first windows is preferably more than 1 and not more than 20. In the first and second aspects, it is especially preferable that the dissimilar substrate be a sapphire substrate having a major surface forming a (0001) plane, and the respective stripes preferably extend in a direction perpendicular to a (11{overscore (2)}0) plane of sapphire; the dissimilar substrate be a sapphire substrate having a major surface forming a (11{overscore (2)}0) plane, and the respective stripes extend in a direction perpendicular to the (1{overscore (1)}02) plane of sapphire; or the dissimilar substrate be a spinnel substrate having a major surface forming a (111) plane, and the respective stripes extend in a direction perpendicular to the (110) plane of spinnel.
Furthermore, in the first and second aspects, growth of the first nitride semiconductor crystal in the step (b) can be performed by metalorganic vapor-phase epitaxy, and a second nitride semiconductor crystal can be grown, on the grown first nitride semiconductor crystal, by a halide vapor-phase epitaxial growth method. Alternatively, the first and second aspects can further comprise the step (c) of forming a second selective growth mask on the first nitride semiconductor grown in the step (b), the second selective growth mask having a plurality of second windows selectively exposing an upper surface of the first nitride semiconductor, and the step (d) of growing second nitride semiconductor portions from the upper surface portions, of the first nitride semiconductor, which are exposed from the second windows, by using a gaseous Group 3 element source and a gaseous nitrogen source, until the second nitride semiconductor portions grown in the adjacent windows combine or unite with each other on an upper surface of the second selective growth mask. In this case, the second selective growth mask preferably has the same arrangement or construction as that of the first selective growth mask.
According to a third aspect of the present invention, there is provided a nitride semiconductor growth method comprising the steps of (a) forming a nitride semiconductor layer on a support member comprising a dissimilar substrate made of a material different from a nitride semiconductor and having a major surface, (b) forming a plurality of recess portions having bottom surfaces substantially parallel to an upper surface of the support member in the nitride semiconductor layer, (c) selectively forming a first growth control mask on a top surface of the nitride semiconductor layer to selectively expose the nitride semiconductor layer from side surfaces of the recess portions, and (d) growing a nitride semiconductor from an exposed surface of the nitride semiconductor layer by using a gaseous Group 3 element source and a gaseous nitrogen source. In this case, the first growth control mask preferably has the same arrangement or construction as that of the first selective growth mask in the first and second aspects.
In the third aspect, it is especially preferable that the step (c) further comprise forming a second growth control mask on the bottom surfaces of the recess portions to selectively expose the nitride semiconductor layer from side surfaces of the recess portions. In this case, the first growth control mask is preferably made up of a plurality of individual or discrete stripes spaced apart from each other, defining the first windows therebetween, and extending parallel to each other. In addition, it is especially preferable that the dissimilar substrate be a sapphire substrate having a major surface forming a (0001) plane, and the respective individual stripes extend in a direction perpendicular to a (11{overscore (2)}0) plane of sapphire; the dissimilar substrate be a sapphire substrate having a major surface forming a (11{overscore (2)}0) plane, and the respective individual stripes extend in a direction perpendicular to the (1{overscore (1)}20) plane of sapphire; or the dissimilar substrate be a spinner substrate having a major surface forming a (111) plane, and the respective stripes extend in a direction perpendicular to the (110) plane of spinnel.
In growing a nitride semiconductor crystal according to the present invention, the gaseous nitrogen source and the gaseous Group III element source are preferably supplied at a molar ratio of not more than 2,000.
In addition, according to the present invention, there is provided a nitride semiconductor substrate comprising a nitride semiconductor crystal and having first and second major surfaces, wherein a region near the first major surface has a relatively small number of crystal defects, and a region near the second major surface has a relatively large number of crystal defects. There is also provided a nitride semiconductor substrate comprising a nitride semiconductor crystal and having first and second major surfaces, characterized by the number of crystal defects in a surface region in the first major surface being not more than 1xc3x97105/cm2.
Furthermore, according to the present invention, there is provided a nitride semiconductor device comprising a nitride semiconductor device structure supported on the nitride semiconductor substrate of the present invention.
Further developments of the present invention are described in the following description and the appended claims.
In the present invention, a nitride semiconductor can be represented by the formula, InaAlyGa1-a-bN (wherein 0xe2x89xa6a,0xe2x89xa6b, and a+bxe2x89xa61).